The World Wide Web: Crash Course Computer Science #30
Summary
TLDRIn this CrashCourse Computer Science episode, Carrie Anne explains the distinction between the Internet and the World Wide Web, emphasizing that the Web operates on top of the Internet. She discusses the foundational elements of the Web, including web pages, hyperlinks, and the importance of hyperlinked information, which was first conceptualized by Vannevar Bush in 1945. The episode covers how web browsers use URLs, DNS lookups, TCP connections, and HTTP to retrieve and display web pages. It also touches on the evolution of web browsers, the development of HTML, and the significance of search engines and Net Neutrality in shaping the modern Web experience.
Takeaways
- đ The World Wide Web is a distributed application that runs on top of the Internet, unlike the Internet itself which is the underlying infrastructure.
- đ Hyperlinks, or links to other pages, are the fundamental building blocks of the web, allowing users to navigate between pages.
- đ Web pages are documents containing content and are the most common type of hypertext document, which can be retrieved and rendered by web browsers.
- đ The concept of hyperlinked information was first conceptualized by Vannevar Bush in 1945 with his Memex machine idea.
- đ A Uniform Resource Locator (URL) is used to specify the unique address of each hypertext page on the web.
- đ» When a web page is requested, a DNS lookup is performed to translate the domain name into an IP address, and then a TCP connection is opened to the web server.
- đ HTTP (Hypertext Transfer Protocol) is used to communicate between the web browser and the web server, with the initial version (HTTP 0.9) having only one command, 'GET'.
- đ Hypertext Markup Language (HTML) was developed to 'mark up' text files with hypertext elements, with the first version (HTML 0.a) created in 1990.
- đ ïž Web browsers are applications that request pages from web servers and render the content, with the first web browser and server created by Tim Berners-Lee in 1990.
- đ Search engines were developed to help users find information on the web, with early engines like JumpStation using web crawlers, indexes, and search algorithms.
- đïž Net Neutrality is a principle that advocates for equal treatment of all internet traffic, preventing ISPs from favoring certain data streams over others.
Q & A
What is the primary difference between the Internet and the World Wide Web?
-The World Wide Web is a distributed application that runs on top of the Internet, which is the underlying infrastructure that conveys data for all applications. The Web is accessed through web browsers and consists of interconnected pages linked by hyperlinks.
What is a hyperlink and how does it function within the World Wide Web?
-A hyperlink is a reference within a web page that points to another web page or resource. It allows users to navigate from one page to another by clicking on text or images that are designated as hyperlinks, creating a web of interconnected information.
Who conceptualized the value of hyperlinked information and what was his hypothetical machine called?
-Vannevar Bush conceptualized the value of hyperlinked information in 1945. He described a hypothetical machine called a Memex, which was intended to create an associative indexing system where items could be automatically linked and retrieved.
What is the full form of HTML and why was it developed?
-HTML stands for Hypertext Markup Language. It was developed to provide a way to 'mark up' text files with hypertext elements, allowing for the creation of web pages with links, headings, lists, and other content that could be interpreted and rendered by web browsers.
What is a URL and how does it relate to accessing web pages?
-A URL, or Uniform Resource Locator, is a unique address for each hypertext page on the web. It specifies the location of a web page and is used by browsers to request pages from web servers using the HTTP protocol.
How does the Hypertext Transfer Protocol (HTTP) facilitate communication between a web browser and a web server?
-HTTP is a protocol used by web browsers to request pages from web servers. When a user requests a page, the browser sends an HTTP command, such as 'GET', to the server, which then responds with the requested hypertext page.
What is the significance of the '200 OK' status code in HTTP?
-The '200 OK' status code in HTTP indicates that the server successfully processed the request and the requested page is being returned. It is a confirmation that the operation was successful and the client can proceed to display the received content.
What is the role of a web browser in accessing the World Wide Web?
-A web browser is an application that enables users to request, retrieve, and render web pages from web servers. It interprets HTML, processes other web technologies like CSS and JavaScript, and displays the content on the user's device.
Who created the first web browser and web server, and what were the fundamental web standards developed at the same time?
-Sir Tim Berners-Lee created the first web browser and web server in 1990 while working at CERN. He also developed the fundamental web standards including URLs, HTML, and HTTP.
What is Net Neutrality and why is it a topic of debate?
-Net Neutrality is the principle that all internet traffic should be treated equally, without any discrimination or preference given to certain types of data. It is a topic of debate because some argue that prioritizing certain types of content could lead to an exploitative business model and stifle innovation, while others believe that market forces and technical requirements might justify different treatment for certain data types.
How did the early search engines like JumpStation work, and what was the basis for their search algorithms?
-Early search engines like JumpStation operated using a web crawler that followed links to gather pages, an index that recorded text terms and their locations, and a search algorithm that consulted the index to return relevant pages based on user queries. The basis for their search algorithms was often the frequency of search terms on a page, which later evolved to include more sophisticated metrics like backlinks from other sites.
Outlines
đ Introduction to the World Wide Web
Carrie Anne introduces the concept of the World Wide Web, distinguishing it from the Internet. She explains that the Web is an application that runs on top of the Internet, similar to how Skype or Instagram operate. The Web is accessed through web browsers and is built on millions of servers worldwide. The fundamental building block of the Web is a single page, which can contain hyperlinks to other pages. Hyperlinks enable users to navigate from one related topic to another, a concept first envisioned by Vannevar Bush in 1945 with his Memex machine. The script also covers the basics of how web pages are retrieved and rendered by browsers, including DNS lookups, TCP connections, and the use of HTTP to request pages from web servers.
đ Hyperlinks and the Evolution of Web Pages
This section delves into the importance of hyperlinks in web pages, which allow for an interconnected web of information. It contrasts the pre-hyperlink era, where users had to manually search for information, with the current system where hyperlinks facilitate easy navigation. The script then explains the technical aspects of web page creation, including the use of HTML tags to structure content and the significance of URLs for locating specific pages. It also touches on the history of web browsers, starting with Tim Berners-Lee's creation of the first browser and server in 1990, and the subsequent development of more sophisticated browsers like Mosaic and the rise of search engines to help users find content on the growing Web.
đ Net Neutrality and the Future of the Web
The final paragraph discusses the concept of Net Neutrality, which is the principle that all data on the Internet should be treated equally. It outlines the debate surrounding this principle, with proponents arguing for equal treatment to prevent ISPs from favoring certain content and opponents suggesting that market forces could regulate any potential abuse. The paragraph also touches on the potential impact of Net Neutrality on innovation and the concerns about ISPs acting as gatekeepers to content. The script concludes by encouraging viewers to learn more about Net Neutrality due to its complex and far-reaching implications.
Mindmap
Keywords
đĄWorld Wide Web
đĄHyperlinks
đĄVannevar Bush
đĄHypertext
đĄUniform Resource Locator (URL)
đĄDomain Name System (DNS)
đĄHypertext Transfer Protocol (HTTP)
đĄHypertext Markup Language (HTML)
đĄWeb Browser
đĄNet Neutrality
Highlights
The World Wide Web is a distributed application running on millions of servers worldwide, accessed via web browsers.
Hyperlinks allow for easy navigation between related information, a concept first proposed by Vannevar Bush in 1945.
Web pages are documents containing content and links to other pages, forming a vast web of interconnected information.
Hypertext, such as web pages, is text containing hyperlinks, retrieved and rendered by web browsers.
Each hypertext page requires a unique address, specified by a Uniform Resource Locator (URL).
When requesting a site, DNS lookup translates a domain name into an IP address, which is then used to open a TCP connection.
HTTP is the protocol used to request and transfer hypertext pages over the internet.
HTML, or Hypertext Markup Language, is used to structure content on web pages with tags for headings, links, and lists.
The first web browser and server were created by Tim Berners-Lee in 1990, establishing foundational web standards.
Mosaic, released in 1993, was the first browser to display graphics alongside text and introduced features like bookmarks.
Search engines like Google use complex algorithms to rank search results based on relevance and backlinks from reputable sites.
Net Neutrality is the principle that all internet traffic should be treated equally, without preferential treatment for certain data.
The debate over Net Neutrality involves concerns about ISPs potentially acting as gatekeepers and stifling innovation.
The rise of the World Wide Web has led to the development of various web browsers and servers, shaping the modern internet landscape.
HTML has evolved significantly, with HTML5 introducing over a hundred tags for a wide range of content and interactive elements.
Additional web technologies like CSS and JavaScript enhance the presentation and functionality of web pages.
Early web search engines used simple metrics for search ranking, which led to manipulation and the need for more sophisticated algorithms.
Transcripts
Hi, Iâm Carrie Anne, and welcome to CrashCourse Computer Science.
Over the past two episodes, weâve delved into the wires, signals, switches, packets,
routers and protocols that make up the internet.
Today weâre going to move up yet another level of abstraction and talk about the World
Wide Web.This is not the same thing as the Internet, even though people often use the
two terms interchangeably in everyday language.
The World Wide Web runs on top of the internet, in the same way that Skype, Minecraft or Instagram do.
The Internet is the underlying plumbing that conveys the data for all these different applications.
And The World Wide Web is the biggest of them all â a huge distributed application running
on millions of servers worldwide, accessed using a special program called a web browser.
Weâre going to learn about that, and much more, in todayâs episode.
INTRO
The fundamental building block of the World Wide Web â or web for short â is a single
page.
This is a document, containing content, which can include links to other pages.
These are called hyperlinks.
You all know what these look like: text or images that you can click, and they jump you
to another page.
These hyperlinks form a huge web of interconnected information, which is where the whole thing
gets its name.
This seems like such an obvious idea.
But before hyperlinks were implemented, every time you wanted to switch to another piece
of information on a computer, you had to rummage through the file system to find it, or type
it into a search box.
With hyperlinks, you can easily flow from one related topic to another.
The value of hyperlinked information was conceptualized by Vannevar Bush way back in 1945.
He published an article describing a hypothetical machine called a Memex, which we discussed
in Episode 24.
Bush described it as "associative indexing ... whereby any item may be caused at will
to select another immediately and automatically."
He elaborated: "The process of tying two things together is the important thing...thereafter,
at any time, when one of those items is in view, the other [item] can be instantly recalled
merely by tapping a button."
In 1945, computers didnât even have screens, so this idea was way ahead of its time!
Text containing hyperlinks is so powerful, it got an equally awesome name: hypertext!
Web pages are the most common type of hypertext document today.
Theyâre retrieved and rendered by web browsers which we'll get to in a few minutes.
In order for pages to link to one another, each hypertext page needs a unique address.
On the web, this is specified by a Uniform Resource Locator, or URL for short.
An example web page URL is thecrashcourse.com/courses.
Like we discussed last episode, when you request a site, the first thing your computer does
is a DNS lookup.
This takes a domain name as input â like âthe crash course dot comâ â and replies
back with the corresponding computerâs IP address.
Now, armed with the IP address of the computer you want, your web browser opens a TCP connection
to a computer thatâs running a special piece of software called a web server.
The standard port number for web servers is port 80.
At this point, all your computer has done is connect to the web server at the address
thecrashcourse.com
The next step is to ask that web server for the âcoursesâ hypertext page.
To do this, it uses the aptly named Hypertext Transfer Protocol, or HTTP.
The very first documented version of this spec, HTTP 0.9, created in 1991, only had
one command â âGETâ.
Fortunately, thatâs pretty much all you need.
Because weâre trying to get the âcoursesâ page, we send the server the following command
â GET /courses.
This command is sent as raw ASCII text to the web server, which then replies back with
the web page hypertext we requested.
This is interpreted by your computer's web browser and rendered to your screen.
If the user follows a link to another page, the computer just issues another GET request.
And this goes on and on as you surf around the website.
In later versions, HTTP added status codes, which prefixed any hypertext that was sent
following a GET request.
For example, status code 200 means OK â Iâve got the page and here it is!
Status codes in the four hundreds are for client errors.
Like, if a user asks the web server for a page that doesnât exist, thatâs the dreaded
404 error!
Web page hypertext is stored and sent as plain old text, for example, encoded in ASCII or
UTF-16, which we talked about in Episodes 4 and 20.
Because plain text files donât have a way to specify whatâs a link and whatâs not,
it was necessary to develop a way to âmark upâ a text file with hypertext elements.
For this, the Hypertext Markup Language was developed.
The very first version of HTML version 0.a, created in 1990, provided 18 HTML commands
to markup pages.
Thatâs it!
Letâs build a webpage with these!
First, letâs give our web page a big heading.
To do this, we type in the letters âH 1â, which indicates the start of a first level
heading, and we surround that in angle brackets.
This is one example of an HTML tag.
Then, we enter whatever heading text we want.
We donât want the whole page to be a heading.
So, we need to âcloseâ the âh1â tag like so, with a little slash in the front.
Now lets add some content.
Visitors may not know what Klingons are, so letâs make that word a hyperlink to the
Klingon Language Institute for more information.
We do this with an âAâ tag, inside of which we include an attribute that specifies
a hyperlink reference.
Thatâs the page to jump to if the link is clicked.
And finally, we need to close the A tag.
Now lets add a second level heading, which uses an âh2â tag.
HTML also provides tags to create lists.
We start this by adding the tag for an ordered list.
Then we can add as many items as we want, surrounded in âL iâ tags, which stands
for list item.
People may not know what a bat'leth is, so letâs make that a hyperlink too.
Lastly, for good form, we need to close the ordered list tag.
And weâre done â thatâs a very simple web page!
If you save this text into notepad or textedit, and name it something like âtest.htmlâ,
you should be able to open it by dragging it into your computerâs web browser.
Of course, todayâs web pages are a tad more sophisticated.
The newest version of HTML, version 5, has over a hundred different tags â for things
like images, tables, forms and buttons.
And there are other technologies weâre not going to discuss, like Cascading Style Sheets
or CSS and JavaScript, which can be embedded into HTML pages and do even fancier things.
That brings us back to web browsers.
This is the application on your computer that lets you talk with all these web servers.
Browsers not only request pages and media, but also render the content thatâs being
returned.
The first web browser, and web server, was written by (now Sir) Tim Berners-Lee over
the course of two months in 1990.
At the time, he was working at CERN in Switzerland.
To pull this feat off, he simultaneously created several of the fundamental web standards we
discussed today: URLs, HTML and HTTP.
Not bad for two months work!
Although to be fair, heâd been researching hypertext systems for over a decade.
After initially circulating his software amongst colleagues at CERN, it was released to the
public in 1991.
The World Wide Web was born.
Importantly, the web was an open standard, making it possible for anyone to develop new
web servers and browsers.
This allowed a team at the University of Illinois at Urbana-Champaign to create the Mosaic web
browser in 1993.
It was the first browser that allowed graphics to be embedded alongside text; previous browsers
displayed graphics in separate windows.
It also introduced new features like bookmarks, and had a friendly GUI interface, which made
it popular.
Even though it looks pretty crusty, itâs recognizable as the web we know today!
By the end of the 1990s, there were many web browsers in use, like Netscape Navigator,
Internet Explorer, Opera, OmniWeb and Mozilla.
Many web servers were also developed, like Apache and Microsoftâs Internet Information
Services (IIS).
New websites popped up daily, and web mainstays like Amazon and eBay were founded in the mid-1990s.
A golden era!
The web was flourishing and people increasingly needed ways to find things.
If you knew the web address of where you wanted to go â like ebay.com â you could just
type it into the browser.
But what if you didnât know where to go?
Like, you only knew that you wanted pictures of cute cats.
Right now!
Where do you go?
At first, people maintained web pages which served as directories hyperlinking to other
websites.
Most famous among these was "Jerry and David's guide to the World Wide Web", renamed Yahoo
in 1994.
As the web grew, these human-edited directories started to get unwieldy, and so search engines
were developed.
Letâs go to the thought bubble!
The earliest web search engine that operated like the ones we use today, was JumpStation,
created by Jonathon Fletcher in 1993 at the University of Stirling.
This consisted of three pieces of software that worked together.
The first was a web crawler, software that followed all the links it could find on the
web; anytime it followed a link to a page that had new links, it would add those to
its list.
The second component was an ever enlarging index, recording what text terms appeared
on what pages the crawler had visited.
The final piece was a search algorithm that consulted the index; for example, if I typed
the word âcatâ into JumpStation, every webpage where the word âcatâ appeared
would come up in a list.
Early search engines used very simple metrics to rank order their search results, most often
just the number of times a search term appeared on a page.
This worked okay, until people started gaming the system, like by writing âcatâ hundreds
of times on their web pages just to steer traffic their way.
Googleâs rise to fame was in large part due to a clever algorithm that sidestepped
this issue.
Instead of trusting the content on a web page, they looked at how other websites linked to
that page.
If it was a spam page with the word cat over and over again, no site would link to it.
But if the webpage was an authority on cats, then other sites would likely link to it.
So the number of what are called âbacklinksâ, especially from reputable sites, was often
a good sign of quality.
This started as a research project called BackRub at Stanford University in 1996, before
being spun out, two years later, into the Google we know today.
Thanks thought bubble!
Finally, I want to take a second to talk about a term youâve probably heard a lot recently,
âNet Neutralityâ.
Now that youâve built an understanding of packets, internet routing, and the World Wide
Web, you know enough to understand the essence â at least the technical essence â of
this big debate.
In short, network neutrality is the principle that all packets on the internet should be
treated equally.
It doesnât matter if the packets are my email or you streaming this video, they should
all chug along at the same speed and priority.
But many companies would prefer that their data arrive to you preferentially.
Take for example, Comcast, a large ISP that also owns many TV channels, like NBC and The
Weather Channel, which are streamed online.
Not to pick on Comcast, but in the absence of Net Neutrality rules, they could for example say that
they want their content to be delivered silky smooth, with high priorityâŠ
But other streaming videos are going to get throttled, that is, intentionally given less
bandwidth and lower priority. Again I just want to reiterate here this is just conjecture.
At a high level, Net Neutrality advocates argue that giving internet providers this
ability to essentially set up tolls on the internet â to provide premium packet delivery
â plants the seeds for an exploitative business model.
ISPs could be gatekeepers to content, with strong incentives to not play nice with competitors.
Also, if big companies like Netflix and Google can pay to get special treatment, small companies,
like start-ups, will be at a disadvantage, stifling innovation.
On the other hand, there are good technical reasons why you might want different types
of data to flow at different speeds.
That skype call needs high priority, but itâs not a big deal if an email comes in a few
seconds late.
Net-neutrality opponents also argue that market forces and competition would discourage bad
behavior, because customers would leave ISPs that are throttling sites they like.
This debate will rage on for a while yet, and as we always encourage on Crash Course,
you should go out and learn more because the implications of Net Neutrality are complex
and wide-reaching.
Iâll see you next week.
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